Most forester-assisted assisted timber sales are based on a 100% field tally of standing trees marked for sale to achieve the objectives of the landowner. Each marked tree slated for sale is then measured for DBH (diameter at breast height) and merchantable log length (total feet or number of 8-ft logs) and then evaluated for grade, defects, and sawlog volume deductions. These estimates are then entered into the forester's tally program to estimate the amount of board feet per tree.
Essentially, there are two kinds of volume scales: standing tree and log.
Tree scale volumes use mathematical formulas based on DBH, Merchantable Height, and Girard Form Class (i.e., tree form/taper; Girard Form Class 78 is commonly used here in Illinois, but there are always exceptions depending on the quality and form of the timber). Tree scale tables (equations) are used when estimating volume in standing timber and are available in Doyle, Scribner, International ¼, and various Girard Form Classes.
Log scale volumes are also based on mathematical formulas, but they are more accurate because they are based on DIB (diameter inside bark based on the small end of the log) and log length. Log scale tables (equations) are used when estimating volume in logs (sawlogs / veneer logs) and are available in Doyle, Scribner, and International 1/4. This is how mills and log buyers buy their logs.
For example: Let’s say you have a standing black walnut tree with a DBH of 24” and it contains four 8-ft sawlogs, but only the first 8-ft sawlog grades as veneer quality. Total board feet estimate for this standing 24” dbh tree = 370 board feet (Doyle) with the following breakdown: 225 board feet of sawlogs and 145 bf of veneer logs in that one 24” dbh tree. This is how most forester-marked timber sales in the Midwest are analyzed and put up for bid.
Hopefully this answered your question!